Particle multipliers

ABSTRACT

A particle multiplier has a chain of dynodes mounted on two stacks of spacers. Each spacer of one of the stacks is of insulating material with a conductive layer at each end and a conductive strip along one side connecting the layers at the ends. Each dynode is electrically connected to the adjacent end layers of two adjacent spacers. The conductive strips constitute resistors so that each dynode is connected to the junction of two resistors of a chain of resistors in series.

United States Patent [191 Ball Aug. 12, 1975 [54] PARTICLE MULTIPLIERS 3,409,84l [H1968 Munn 33l/34 3,458,745 7 1969 Sh ld [76] Inventor: Geoffrey William Ball, Apple Patch, $684910 1, f jf n mugs Bellingdon, Chesham Buckmghamshlre' England Primary Examiner.lohn Kominski [22] Filed; Dec. 29, 1972 Attorney, Agent, or Firm-Toren, McGeady and 2| Appl, No.: 319,702 stinger [57] ABSTRACT [52] 3l3/l05; 313/250; 3 ]3/268 A particle multiplier has a chain of dynodes mounted [5 [1 Int. Cl. H01 43/10 on two stacks of Spacers. Each Spacer of one of the {58) Field of Search .t 313/104, I05, 250, 268; 4

stacks 18 of insulating material with a conductive layer 331/34 at each end and a conductive strip along one side con- References Cied nectmg the layers at the ends. Each dynode is elect r1- cally connected to the ad acent end layers of two ad a- UNITED STATES PATENTS cent spacers. The conductive strips constitute resistors 2,622,218 l2/l952 Jenny 7. 313/105 so that each dynode is connected to the junction of 2.866.9l4 12/)958 Lallemand 313/ two resistors of a chain of resistors in series 3,| 24044 12/!963 Stemglasstm. 3l3/l04 -2129,! l/l966 Bartschat 313/!05 8 laims, 6 Dra ing Fi ures tAltNitu AUb I ram FlClb.

FIGS.

PARTICLE MULTIPLIERS This invention relates to particle multipliers.

Conventional particle multipliers, which may be ion or electron multipliers, are used to greatly multiply an electron or ion flow. A particle multiplier is, for example, normally incorporated in a mass spectrometer. A particle multiplier comprises a target and a number of dynodes that is to say, electrodes coated with a material which exhibits the phenomenon of secondary emission and a collector. Assuming the particle multiplier is an ion multiplier, an input ion strikes the target and causes secondary emission therefrom of electrons. The electrons emitted by the target are attracted to and strike the first dynode of the chain. This causes, by secondary emission, the emission of electrons by the first dynode which are attracted to the second dynode and this cycle continues until the final dynode which emits electrons which are collected by the collector. The first dynode is at a negative potential with respect to the second dynode, in turn at a negative potential with respect the third dynode etc. To provide the potentials required for all the dynodes, there is provided a resistor chain connected between a supply line and earth and each dynode other than the first is connected to an appropriate point in the chain.

It is an object of this invention to provide an improved particle multiplier.

According to this invention there is provided a particle multiplier comprising a chain of dynodes mounted on a stack of spacers, each spacer being of insulating material with a conductive layer formed at each end and a conductive layer along its side connecting the layers at each end, each dynode being electrically connected to the adjacent end layers of two adjacent spacers. The conducting layer along the side of each spacer acts as a resistor.

Preferably each dynode is integral with or is secured to a plate located between the adjacent end layers of two adjacent spacers.

Preferably the layer along the side of each spacer is a strip whose area is reduced to increase its resistance. Suitably the area of each strip is reduced by blasting with abrasive material.

A particle multiplier in accordance with this invention will now be described, by way of example only, with reference to the accompanying drawings, of which:

FIG. I is a schematic view of a known particle multiplier;

FIG. 2 is a schematic view of a particle multiplier in accordance with this invention;

FIG. 3 is a perspective view of a spacer of the particle multiplier shown in FIG. 2;

FIG. 4 is an end view of an alternative spacer; and

FIGS. 5 and 6 are, respectively end and side views of another alternative spacer.

Referring first to FIG. 1, the arrangement schematically shown therein is of any conventional particle multiplier which comprises a target 1 opposite an aperture 2 through which ions enter the particle multiplier and strike the target I which is covered with a material which exhibits secondary emission.

A chain of dynodes 3 are provided, the dynodes being schematically illustrated as being in two columns facing each other; the dynodes may be bucket shaped. Twelve dynodes are shown in the drawing but the number may differ and may for example be fourteen. The dynodes 3 are connected to different points in a resistor chain of resistors 4 connected between earth and a negative potential of say, 2 to 4 KV. At the end of the dynode chain opposite to the target 1 there is provided a collector 5 held at a positive potential. The target I is identical to the dynodes 3.

In use, an ion enters the particle multiplier through the aperture 2 and strikes the target 1 which emits electrons. These electrons are attracted to the first dynode 3 of the chain of dynodes which is at a potential positive with respect to the target 1 and the electrons strike the first dynode which then emits electrons due to secondary emission. The electrons emitted by the first dynode are attracted to the second dynode because it is at a more positive potential and strike it so that it is caused to emit electrons by secondary emission. This process is repeated along the chain of dynodes, the number of electrons emitted by each succeeding dynode being increased. The electrons emitted by the final dynode 3 are attracted to the collector 5 and are measured in an external circuit.

A particle multiplier in accordance with this invention is illustrated in FIG. 2, in which ten bucket shaped dynodes ll, numbered from 1 to 9 are provided. A plate 12 is secured to each dynode I1 and is supported by two spacer stacks l3 and 14. Each spacer stack comprises a ceramic rod 15 which passes through ten ceramic spacers 16, the plate 12 of each dynode other than dynode 1 being disposed between two adjacent spacers 16 in engagement with the adjacent end faces of those spacers l6 and being formed with apertures (not shown) through which the rods 15 pass. Dynode 1 acts as the target, is provided with a grid 17 and its plate 12 rests on top of the top spacer 16 of each stack. The spacers 16 of the stack 13 are entirely of ceramic material but those of the stack 14 are as illustrated in FIG. 3; all the spacers 16 are approximately cubical as can be seen. As shown in FIG. 3 each spacer 16 is formed with a central aperture 18 through which the ceramic rod 15 passes. Each of the opposed faces of the ceramic spacer 16 in which the aperture 18 is formed is covered by a layer 19 of conductive material, e.g. gold, and the layers 19 at the opposed faces of the spacer 9 are connected by a metallic strip 20 along one side of the spacer 16. The spacer 16 is placed between two electrodes which contact the layers 19 and the resistance of the strip 20 is measured while abrasive material under air pressure is blown against the strip 20 to reduce its area until its resistance increases to the desired value which may be I or 2 M ohms. The ceramic material may be high purity luminar.

It will be appreciated that in the construction shown it is unnecessary to utilise separate resistors which is very advantageous.

The alternative ceramic spacer illustrated in FIG. 4 has a central relatively larger aperture 21 and a smaller aperture 22 at each end. These spacers are stacked using narrow rods passing through apertures 22. When used in stack 13 the spacer shown in FIG. 4 has no conductive layer and when used in stack 14 its end faces are covered with a layer similar to layer 19 whereas on one side face a metallic strip corresponding to metallic strip 20 is formed.

The spacer shown in FIGS. 5 and 6 only differs from spacer 16 in that it is cylindrical. The area of strip 20 removed in the manner previously described is indicated at 23.

The invention is applicable to photo multipliers.

I claim:-

1. in a particle multiplier having a plurality of dynodes generally arranged in a first direction, a plurality of serially connected resistive elements, and means for electrically connecting successive ones of the dynodes to the junctions of successive ones of the resistive elements, the improvement wherein (A) the resistive elements comprise a stack of spacers successively arranged in the first direction and formed from insulating material, the opposed ends of each spacer in the first direction being provided with a conductive layer, the side of each spacer between the conductively coated ends being provided with a resistive layer interconnecting the conductive layers on the ends to form a resistive body, and wherein (B) the connecting means position each dynode between and in contact with the conductive layers on the opposed ends of a separate pair of adjacent spacers.

2. A particle multiplier as claimed in claim 1 wherein each dynode is electrically and mechanically connected to a plate located between the adjacent end layers of two adjacent spacers.

3. A particle multiplier as claimed in claim 1 wherein the layer along the side of each spacer is a strip whose area is reduced to increase its resistance to a required value.

4. A particle multiplier as claimed in claim 3 wherein the area of each strip is reduced by blasting with abrasive material.

5. A particle multiplier as claimed in claim 2 which comprises a further stack of insulating spacers, each plate being located between two adjacent spacers of the further stack.

6. A particle multiplier as claimed in claim 1 wherein the stack of spacers comprises a rod which passes through aligned holes in the spacers.

7. A particle multiplier as claimed in claim 2 wherein the further stack of spacers comprises a rod which passes through aligned holes in the spacers.

8. A particle multiplier comprising a chain of dynodes mounted on a stack of spacers and a chain of resistors connected in series, each dynode being electrically connected to the junction of two adjacent resistors of the chain of resistors, each spacer being of insulating material and provided with a conductive layer at each end and with a resistive layer along its side which connects the end conductive layers and constitutes a resistor of the chain of resistors, each dynode being electrically connected to the adjacent end conductive layers of two adjacent spacers. 

1. In a particle multipLier having a plurality of dynodes generally arranged in a first direction, a plurality of serially connected resistive elements, and means for electrically connecting successive ones of the dynodes to the junctions of successive ones of the resistive elements, the improvement wherein (A) the resistive elements comprise a stack of spacers successively arranged in the first direction and formed from insulating material, the opposed ends of each spacer in the first direction being provided with a conductive layer, the side of each spacer between the conductively coated ends being provided with a resistive layer interconnecting the conductive layers on the ends to form a resistive body, and wherein (B) the connecting means position each dynode between and in contact with the conductive layers on the opposed ends of a separate pair of adjacent spacers.
 2. A particle multiplier as claimed in claim 1 wherein each dynode is electrically and mechanically connected to a plate located between the adjacent end layers of two adjacent spacers.
 3. A particle multiplier as claimed in claim 1 wherein the layer along the side of each spacer is a strip whose area is reduced to increase its resistance to a required value.
 4. A particle multiplier as claimed in claim 3 wherein the area of each strip is reduced by blasting with abrasive material.
 5. A particle multiplier as claimed in claim 2 which comprises a further stack of insulating spacers, each plate being located between two adjacent spacers of the further stack.
 6. A particle multiplier as claimed in claim 1 wherein the stack of spacers comprises a rod which passes through aligned holes in the spacers.
 7. A particle multiplier as claimed in claim 2 wherein the further stack of spacers comprises a rod which passes through aligned holes in the spacers.
 8. A particle multiplier comprising a chain of dynodes mounted on a stack of spacers and a chain of resistors connected in series, each dynode being electrically connected to the junction of two adjacent resistors of the chain of resistors, each spacer being of insulating material and provided with a conductive layer at each end and with a resistive layer along its side which connects the end conductive layers and constitutes a resistor of the chain of resistors, each dynode being electrically connected to the adjacent end conductive layers of two adjacent spacers. 